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Terahertz bomb sniffer wins student prize

Photonics SpectraMay 2011
TROY, N.Y. – A new detection method extends
the distance from which powerful terahertz technology can remotely sniff out hidden
explosives, chemicals and other materials.

Benjamin Clough, a doctoral student at Rensselaer Polytechnic
Institute, has developed a technique that uses sound waves to boost the effective
distance of terahertz spectroscopy from a few feet to several meters. For the innovation,
Clough was named winner of the 2011 $30,000 Lemelson-MIT Rensselaer Student Prize,
which is awarded annually to a Rensselaer senior or graduate student who has created
or improved a product or process, applied a technology in a new way, redesigned
a system or demonstrated remarkable inventiveness in other ways.

Benjamin Clough, a doctoral
student at Rensselaer Polytechnic Institute, has developed a method for extending
the distance from which terahertz technology can detect explosives, chemicals and
other hazardous materials. Courtesy of Kris Qua, Rensselaer.
Clough’s method circumvents a fundamental limitation of
remote terahertz spectroscopy, which is that it works at only short distances,
so it has not been suitable for detecting bombs or hazardous materials.

His method uses sound waves to remotely “listen” to
terahertz signals and identify a target. First, two laser beams are focused into
the air to create small bursts of plasma, which in turn create terahertz pulses.
Second, another pair of lasers is aimed near the target to create a second plasma,
which detects the terahertz pulses from the first two laser beams after they have
interacted with the material. The detection plasma produces acoustic waves as it
ionizes in the air.

Using a sensitive microphone to listen to the plasma, Clough detected
terahertz wave information embedded in the sound waves. The information was converted
into digital data and checked against a library of known terahertz fingerprints
to determine the target’s chemical composition.

Using acoustics, Clough has identified terahertz fingerprints
from several meters away. Separately, he has demonstrated plasma acoustic detection
from 11 m, a distance limited only by available lab space.